One known example of a conventional grip-type cutter knife is illustrated in FIGS. 1 and 2. The conventional grip-cutter knife 10 comprises an elongated cutter body 11 provided with a grip portion 12. At the front end of the body 11, a circular rotary blade 15 is provided. As illustrated in FIG. 1, the rotary blade 15 is projected from the body for cutting. As illustrated in FIG. 2, the rotary blade 15 is retracted in the body, and cutting is not possible.
The rotary blade 15 is connected to a swing member which is pivotably supported in the cuter body 11. A part of this swing member is projected from the grip portion 12 to serve as a trigger lever 14, as illustrated in FIG. 2. The swing member is forced into the non-cutting position by a spring member arranged in the cutter body 11. When grasping the trigger lever 14 into the cutter body 11 against the force exerted by the spring, the rotary blade 15 is projected from the forward end of the cutter body 11. When releasing the grasping hand, the rotary blade 15 is retracted into a platform 13 at the forward end of the cutter body.
FIGS. 3 to 5 are perspective views showing another example of a conventionally known cutter knife that in addition to having all the elements described above in connection with the knifes of FIGS. 1 and 2, is provided as well with a push-lock button 30.
The lock button 30 may be constituted by a cylindrical locking member. The height, or length, of the lock button is equal to the sum of the cutter body thickness and the thickness of an upward projection of the lock button. When the lock button 30 is pushed into the cutter body 21 the lock button is downwardly projected from the backside of the cutter body 21. When the lock button 30 is upwardly projected, as illustrated in FIG. 3, the swing of the swing member 44 is blocked so that the rotary blade 55 cannot descend.
When the lock button 30 is pushed into the cutter body so as to project downwardly, the rotary blade 55 can freely move when grasping or releasing a grip portion.
It is conventionally known that a cutter knife comprises two body pieces and a swing member sandwiched in between the body pieces. The two body pieces constitute the cutter body, and in the knife configurations known in the art, the swing member caries the rotary blade 55, and one end of the swing member serves as a trigger lever 44.
A body piece has a configuration corresponding to that of a cutter body 21. The body piece is at its front end provided with a platform 230, as illustrated in FIG. 5, which accommodates the rotary blade 55. At the center of the platform 230, an elongated circular opening 231 is formed for allowing the rotary blade to slide. At the opposite side of the platform 230 an elongated grip portion is arranged. Between the platform 230 and a grip portion 210 a circular opening 220 is formed for holding the cylindrical locking member 30 in the thickness direction of the cutter body 21.
As it may be observed in connection with the configurations of the cutting knife shown in FIGS. 1 to 5, irrespective that the blade is in a lowered position or in a retracted position, the blade is exposed at all times. Thus injury may easily occur as a result of incorrect handling of the cutter knife. Further, while in operation, for cutting materials that tend to slip on the cutting surface, where the operator might need to secure with its hands in position the material to be cut, the risk of injury to the hands of the operator is increased since no protective surface prevents the hands of the operator from touching the blade. Further yet, since in the configurations known in the art the blade is exposed at all times, the blade edge may be easily damaged, e.g. by denting.